The use of concrete lined, grate or solid covered trenches are well known in the road, parking lot, and manufacturing plant construction industry. The typical trench construction includes a pair of spaced rails, wherein each rail has a grate supporting surface upon which a central grate rests. FIGS. 1 and 2 illustrate a typical prior art trench-forming assembly 10. Each rail 12, 14 is made of a rigid material which preferably can be easily and inexpensively molded, cast, extruded, or stamped into a desired rail shape. As indicated in these figures, each rail 12, 14 can be Z-shaped in cross-section and connected by a connecting rod 16 which typically is attached to the rails by welding to an inside surface 17 of each rail. When such connecting rods 16 are used, at least two such connecting rods are placed between each set of rails, typically with one rod positioned at the end of each rod pair. The connecting rods 16 are used to maintain the rails 12, 14 in a fixed position relative to each other prior to and during the curing of the hardenable material used to form the completed trench.
Adjustable anchoring means typically are used to adjust the slope and height of the rails 12, 14. As indicated in FIGS. 1 and 2, one such means includes a connecting member 18 that extends outwardly from an outside surface 20 of the rails 12, 14 to connect to an anchor rod 22 that is adapted to be driven into the ground at the bottom of the excavated trench. As is further indicated in the figures, the connecting member 18 includes a collar 24 through which the rod 22 can be passed. Each collar 24 includes a fastening member such as a thumb screw 26 which is threadingly inserted into an aperture formed within each collar so that, when the fastening member is tightened, the connecting member 18 can be fixed relative to the rod 22 such that the rails 12, 14 can be supported by the rods in the desired position.
The prior art assembly 10 of FIGS. 1 and 2 further includes a form 28. Although capable of alternative construction, the form 28 typically is made of an expanded polystyrene foam which is adapted to be held in a fixed position between the rails 12, 14. The form 142 normally includes an upper surface 30 and a shaped lower surface 32. The lower surface 32 can be shaped into any contour, but preferably is tapered from the upper surface 30 to facilitate simple removal from the final trench. In the embodiment illustrated in FIGS. 1 and 2, a plurality of grooves 34 are formed in the upper surface 30 of the form 28 to receive each connecting rod 16 provided along the rails 12, 14. The grooves 34 allow each connecting rod 16 to laterally traverse the form 28 to secure the form 28 in position while held between the rails 12, 14 as shown in FIG. 2. Once the assembly is arranged as illustrated in FIG. 2 and the anchoring means adjusted into the desired position, hardnenable material (typically concrete) is poured into the excavated trench to surround the form 28. After the hardenable material has cured, the form 28 can be removed to reveal a completed trench having the contours of the lower surface 32 of the form 128. To facilitate removal of the form 28, however, the connecting rods 16 first must be removed from the rails 12, 14. In that the connecting rods 16 usually are welded to the rails, the rods typically must be cut from the rails with an electric grinder or saw.
Although adequately functional in design, there are several disadvantages associated with the prior art forming system set out in FIGS. 1 and 2. First, the upward buoyancy forces exerted on the form 28 often is sufficient to deepen the grooves 34 which receive the connecting rods 16. As a result, the form 28 can be displaced upwardly, resulting in an uneven trench bottom surface. This result is particularly disadvantageous to the liquid displacing function of the trench in that it can create stagnant puddles of liquid therein. Furthermore, the connecting rods 16 can deform into an upwardly convex orientation, especially in wider form applications, due to the buoyancy forces imposed by the hardenable material. This deformation can cause misalignment or twisting of the frames, and can result in an uneven bottom trench surface, as described above.
Another disadvantage associated with the assembly illustrated in FIGS. 1 and 2, and other similar known systems, pertains to the attachment and removal of the connecting rods. Specifically, additional labor is required to weld each of the rods between the rails, which increases the cost and complexity of the assembly and makes it less economical to manufacture. In addition to the unnecessary labor associated with attachment of the connecting rods, additional labor is needed to remove them. Because the connecting rods normally must be cut away from the rails, the welded rod feature requires the presence of electrical power on a construction site or the use of gasoline powered tools. In the absence of such equipment, a hack saw must be used, making the removal of the form extremely labor intensive and quite expensive.
From the above, it can be appreciated that it would be advantageous to have a form assembly which is more resistant to the buoyancy forces imposed by the hardenable material, and which is less difficult to use.